Hydroxylation state

A fully hydroxylated state in which all the OH groups are bound to Si atoms (with N(OU) = 4.6 OH nm-2) would correspond to the octahedral, (111), face of /J-cristo-balite or the basal face of /J-tridymite. However, as indicated in Table 10.5, the surface hydroxyl concentrations found on some arc and fume silicas are significantly lower, typical values being in the range 3.4-4 OH nm 2 (Baker and Sing, 1976 Unger, 1979, p. 62 Gallas et al., 1991). 

More recently, it was found that the hydroxylation state of the alumina has a determining influence upon the particle size of platinum crystallites. Controlled dehydroxylation of the alumina proved to be the most reliable method for preparing stable catalysts with gradual variations of the dispersion, and a continuous series of Pt/Al2O3 catalysts with dispersions (characterized by the H/Pt ratio) ranging from 0.04 to 1.0 was prepared by... 

Planet, and, microbial responses with the sucroae esters. In addition to the above we have conducted experiments on the effects of the sucrose esters on plants and microorganisms and we report these data for the first time. However it should be reiterated that the sucrose esters were composed of acetic (C2) 2- and 3-methylbutyric (C5) and 3-methylvaleric (C6) acids and only the glucose molecule was ester if ied the fructose portion remained in the free hydroxyl state. Also the sucrose esters were extremely difficult to separate so that mixtures were initially obtained and tested. We shall see in the wheat coleoptiles bioassay that as the number of 3-methylvalerate residues decreases in the glucose moiety so the level of biological activity decreases at the 10 4 M level though in all cases there is 100Z inhibition at 10 3 m (Figure 7). 

The maximum hydroxylated state of the surface of Si02 samples (the degree of surface coverage with OH groups,... 

S Additional information <2, 10> (<10> enzyme interacts with XRCCl, a scaffold protein that helps recruit repair enzymes at sites of single-strand breakage [27] <2> in vivo role is possibly in maintaining DNA or RNA in the 5 -phosphorylated 3 -hydroxylated state which is the substrate for many reactions such as ligation and packaging [1]) [1, 27]... 

Rehydroxylation occihs and silanol groups are formed when the dehydroxylated silica surface reacts with water in a vapor or liquid state. Complete rehydroxylation was once thought possible only in samples that had been subjected to preliminary treatments at temperatures below 400°C. Rehydroxylation of silica samples activated at temperatures in the range of 400°C to 1000-11(X)°C is now known to be completely restored to the maximum hydroxylated state (ooh = 4.6 OH groups per square nanometer) by treatment with water at room temperature. For samples subjected to extensive dehydroxylation, more... 

The comparison of the results obtained by the author [3-5] with those reported in the literature covers the following topics (i) limiting temperature for removing physically adsorbed water from the hydroxylated surface (ii) completely hydroxylated state of the surface (iii) dehydroxylation of the surface (iv) rehydroxylation of the surface (v) stmcturally bound water inside silica particles. Owing to the lack of space in this abstract, references are made only to those results which closely... 

In the 1950s, A. Kiselev, Zhdanov, and co-workers [12,84,155-159] showed that when the adsorption isotherms of water are expressed as absolute isotherms (referred to as the unit surface of the Si02 sample), widely different forms of amorphous silica having a completely hydroxylated state adsorb the same amount of water at the same relative pressure (p/po < 0.3). Thus the plots of absolute adsorption isotherms for different samples showed that the surfaces of these samples are of a similar nature. The adsorption properties of non-porous silica and silica having large pores (i.e., an absence of micropores) depend above aU on the presence of OH groups and on the degree of hydroxylation of the surface. 

The number of bound phosphates can vary in a nucleotide. When phosphate is absent, the molecule is referred to as a nucleoside or a deoxynucleoside, depending on the hydroxylation-state of the sugar. Up to three phosphate groups can be present. When one or more phosphates are present, the compound is commonly referred to by the base present, how many phosphates are present, and whether the deoxy-form of the sugar is used. For example, when the base adenine is present and there are two phosphates, the corresponding deoxyribonucleotide and ribonucleotide are typically referred to by the abbreviations, dADP and ADR The former and latter abbreviations indicate deoxy-adenine diphosphate and... 

Gonzalez-Elipe, A.R., Espinos, J.P., Eernandez, A., and Munuera, G. XPS study of the surface carbonation hydroxylation state of metal-oxides. Appl. Surf. Sci. 1990, 45, 103-108. 

As has been described above, the heterogeneity of the Lewis sites essentially arises from the partially hydroxylated state of many of the aluminum fluorides. A greater... 

Sulphur dioxide (pK = 1.89) is another molecule commonly used to investigate basicity of solid catalysts. SO2 adsorption on the surface of metal oxides is complex. Several types of species can be formed according to hydroxylation state and the acidity or basicity of surface [58]. Interaction of SO2 with basic 0 leads to formation... 

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